Elevator chair mechanisms that assist user entry and exit from a seat portion of the chair, while initially successful in the nursing home and clinic marketplaces have only recently achieved some degree of success in the residential marketplace. Formerly believed desirable only for patients with severe lower extremity immobility, today such chair elevator or lift systems have found acceptance by users with significantly lesser handicaps including those with simply inflammatory arthritis in the lower extremity joints and other orthopedic maladies commonly found in people over 50 years of age.
In the residential market of course the chair mechanism must be aesthetically acceptable and complementary to the home environment which necessitates the motor drive assembly be compact and located where it may be easily covered by upholstery. It also requires the lift linkages or arms be similarly located to be easily concealed by fabric. More importantly, the linkage or actuator assembly for the chair should have a low power requirement in order to reduce the size of the drive motor necessary, and decreased power consumption to provide a lift chair at a lower cost than formerly available.
There have been a plurality of attempts at designing such chair mechanisms and one is shown in the Gaffney, U.S. Pat. No. 3,250,569 which shows a conventional home-style lounge chair where the seat moves upwardly and tilts forwardly to facilitate user exit. The design is compact and has a few number of links and for that reason it is for the most part acceptable in the residential market. However in this chair only the seat elevates and the back remains in a stationary position with the arms, so the user has some apprehension in entering and exiting the chair because in the entry and exit position the user cannot contact the back at all and the arms are in a very depressed position relative to the seat.
There are however seat mechanisms designed in the past where the arms and back move upwardly and forwardly and one is illustrated in the Gaffney, U.S. Pat. No. 4,083,599. In this design the seat, back and arms are one unitary assembly all stationary with respect to one another and the chair is raised and lowered by a pair generally parallel arms generally horizontally disposed fixed at the rear to a stationary frame plate and at the front to a lift frame for the chair. The actuator is a screw drive and also acts as a third extending link connected at the rear to the same frame and at its front end to the forward center portion of the chair frame. This parallelogram type linkage has high power requirements and thus necessitates an excessively large motor for the residential marketplace. Also the location of the various links underneath the chair frame require a substantial amount of additional upholstery to cover the linkage mechanism and provide a safe actuation system.
The Gorden, U.S. Pat. No. 2,608,239 shows a threaded screw actuator that raises and lowers a chair back bar with side members slidable in generally vertical grooves in vertical rails. The Gorden chair lifts as a unit and has no seat tilting.
The Yates, et al., U.S. Pat. No. 3,343,871 shows an automatically operated invalid chair that has a reclining back and a seat frame that moves with a slotted follower mechanism to lift and seat tilt positions. There is no upward movement of the front portion of the seat upon lift.
The Gaffney, U.S. Pat. No. 4,007,960 discloses a mechanism for back to seat articulation, ottoman extension and chair lift. As in the above Gaffney patent, the actuator assembly and linkage is disposed entirely underneath the seat demanding very high power requirements and this chair has problems with exposed linkages and upholstery around the linkage mechanism under the seat. Furthermore, as in the above Gaffney elevator chair, the seat back tilts forwardly upon lift which is not really desirable.
The Randolph, U.S. Pat. No. 4,077,483 shows a track-type invalid vehicle where the seat is movable to a raised position with a generally vertical threaded screw. The screw lifts the entire chair, and there is no seat to back articulation or seat tilting.
The Andreasson, U.S. Pat. No. 4,249,774 shows a chair lift mechanism, but in this device while the seat articulates, it does so in two pieces and there is no articulation between the seat portion and the back portion.
The Booth, U.S. Pat. No. 4,545,616 shows a lift mechanism for a mobile chair with elevating seat where the seat is raised by a vertical screw that lifts the seat back. It does show articulation between the chair back and the seat frame with a generally parallelogram type linkage. Because of this four bar linkage, the back of the chair moves relatively toward the front of the seat as the chair is lifted. This is permitted by wheels that support a front link of the chair in one embodiment and the seat back in another embodiment, both designed for horizontal translating movement.
The Krauska, U.S. Pat. No. 4,852,939 shows a device for converting or retrofitting a recliner chair to a recliner lift chair with a mechanism somewhat similar to the mechanism shown in the Gaffney, U.S. Pat. No. 4,007,960 described above, except that it does appear that Krauska's arms articulate relative to the seat. Krauska does not include any chair back to seat articulation and note that the seat frame is pivotally mounted by spaced short links on a control rail that scissors with the seat frame to effect ottoman scissor linkage movement.
It is a primary object of the present invention to ameliorate those problems noted above in chair assemblies that provide for seat lifting to facilitate entry and exit from the chair.